Conventional lithium rechargeable batteries generally have charge cut-off voltages of about 4.2 V (vs. Li) depending on the oxidation resistance of the non-aqueous electrolyte. When charged to over 4.2 V (vs. Li), the positive electrode potential increases, thereby decomposing the non-aqueous electrolyte. Accordingly, the cycle and battery characteristics of the lithium rechargeable battery deteriorate at high temperatures. However, lithium rechargeable batteries have improved energy density at charging voltages of over 4.2 V and average operating voltages are also increased.
Recently, a non-aqueous electrolyte with high voltage resistance was disclosed in Japanese Patent laid-open No. 9-167635, the entire content of which is incorporated herein by reference. The high voltage resistant electrolyte was achieved by using a sulfurous acid ester and a halogenated alkyl group as the electrolyte solution. However, despite the improved voltage resistance of the electrolyte solution, lithium ion conductivity of the battery is drastically reduced.